CA2050783A1 - Process for the preparation of 2-mercaptobenzothiazole - Google Patents
Process for the preparation of 2-mercaptobenzothiazoleInfo
- Publication number
- CA2050783A1 CA2050783A1 CA002050783A CA2050783A CA2050783A1 CA 2050783 A1 CA2050783 A1 CA 2050783A1 CA 002050783 A CA002050783 A CA 002050783A CA 2050783 A CA2050783 A CA 2050783A CA 2050783 A1 CA2050783 A1 CA 2050783A1
- Authority
- CA
- Canada
- Prior art keywords
- carbon disulphide
- process according
- reaction
- pressure
- mbt
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D277/00—Heterocyclic compounds containing 1,3-thiazole or hydrogenated 1,3-thiazole rings
- C07D277/60—Heterocyclic compounds containing 1,3-thiazole or hydrogenated 1,3-thiazole rings condensed with carbocyclic rings or ring systems
- C07D277/62—Benzothiazoles
- C07D277/68—Benzothiazoles with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached in position 2
- C07D277/70—Sulfur atoms
- C07D277/72—2-Mercaptobenzothiazole
Abstract
Abstract:
The invention relates to a process for the preparation of 2-mercaptobenzothiazole from aniline, sulphur and carbon disulphide under pressure and the separation of the 2-mercaptobenzothiazole from the crude reaction product by cooling and recycling the by-products into the reactor together with aniline, sulphur and carbon disulphide, the reaction being carried out using a residence time in the reactor of at least one hour at temperatures of 220 - 280°C and said reaction being discontinued before the reaction equilibrium is reached and a maximum hydrogen sulphide pressure being maintained on cooling by mixing the crude reaction product with carbon disulphide at above 100°C and the hydrogen sulphide being removed completely only after the crystallisation of the 2-mercaptobenzothiazole.
The invention relates to a process for the preparation of 2-mercaptobenzothiazole from aniline, sulphur and carbon disulphide under pressure and the separation of the 2-mercaptobenzothiazole from the crude reaction product by cooling and recycling the by-products into the reactor together with aniline, sulphur and carbon disulphide, the reaction being carried out using a residence time in the reactor of at least one hour at temperatures of 220 - 280°C and said reaction being discontinued before the reaction equilibrium is reached and a maximum hydrogen sulphide pressure being maintained on cooling by mixing the crude reaction product with carbon disulphide at above 100°C and the hydrogen sulphide being removed completely only after the crystallisation of the 2-mercaptobenzothiazole.
Description
7~
Process f~r the preparation of 2-mercaptobenzothiazole Akzo Patente GmbH
Wuppertal * * *
Description:
The present invention relates to a process for the preparation of 2-mercaptobenzothiazole from aniline, carbon disulphide and sulphur.
Process f~r the preparation of 2-mercaptobenzothiazole Akzo Patente GmbH
Wuppertal * * *
Description:
The present invention relates to a process for the preparation of 2-mercaptobenzothiazole from aniline, carbon disulphide and sulphur.
2-Mercaptobenzothiazole (MBT) is a starting material which is industrially very important for the preparation of vulcanisation accelerators such as, for example, dibenzothiazolyl disulphide and sulphenamides.
Industrially, M~T is generally produced by the Kelly process (US Patent 1,631,871), in which aniline, carbon disulphide and sulphur are reacted under elevated pressure at elevated temperatures. The resulting crude MBT must then be purified to remove unconverted starting compounds, intermediates and products from secondary reactions. The MBT purification which is customary industrially in principle consists of a reprecipitation, in which the crude MBT is dissolved in sodium hydroxide solution and the tar-like by-products are decanted off, filtered off or extracted. The aqueou~ sodium MBT solu- -tion is subjected to a further oxidative treatment, if appropriate; the MBT is then precipitated using sulphuric acid and filtered off (cf. German Patent 2,258,484).
The disadvantage~ of a purification of this ~ype are that the aqueous phase contains about 85 kg of Na2SOs per lOQ kg of MBT formed, which ha3 to be disposed of with the effluent. In addition, about 15 kg of waste products (tars~ are produced per 100 kg of MBT and the bulk of these waste products has to be disposed of as solid waste, for example by means of combustion. A
considerable proportion of the by-products also passes into the effluent, where it causes a high chemical oxygen demand. The chemical oxygen demand (COD) is determined in mg/l 0z by back-titration of dichromate. The analytical 7 ,', methods vary and must be indicated with the result.
In addition, in the case of modern catalytic oxidation processes using oxygen to form MBTS and sul-phenamides (compare German Patent 3,113,298 and, respec-tively, German Patent 3,325,724) a high purity of the MBT
is required because it is then possible to work with very low catalyst concentrations. Such a purity is not guaran-teed with the conventional production methods for MBT.
Those skilled in the art have therefore made many attempts to prepare MBT both in high purity and in high yield. Thus, US Patent 3,031,073 describes another process for the preparation of MBT, in which aniline, carbon disulphide and sulphur are heated under pressure in a cyclic procedure, the pressure is reduced, the ~BT
is removed from the crude product, the residue is mixed with the necessary amount of aniline, carbon disulphide and sulphur and this mixture is again heated to form MBT.
Any method is said to be suitable for isolation of MBT
from the crude reaction product. This patent specification pays detailed attention to a purification method using water/carbon disulphide emulsions, which incidentally also contain a surface-active substance.
However, according to Example 1 of the said US
Patent Specification 3,031,073, it is also possible to use carbon disulphide on its own as purifying agent.
After a reaction time of 5 hours at 245C, the reaction is discontinued by letting down the pressure and removing the reaction mixture from the autoclave. With this procedure the pre~sure generated by hydrogen sulphide is entirely removed by letting down to atmospheric pressure.
In order to purify the crude product, the latter is mixed with carbon disulphide in an autoclave and the mixture is heated to 140C and kept at this temperature for 30 to 45 minutes. Finally, based on the purification method, MBT
is obtained in a yield of 94% and in a purity which i8 indicated as 99.5%. When thiq procedure was repeated, a total yield of 82~ was obtained. The MBT had a purity of 98%.
DE-OS (German Published Application) 2,652,394 describes a process for the purification of crude MBT
using carbon disulphide. According to Example 1, aniline, carbon disulphide and sulphur are allowed to react for 50 minutes at 220C and the hydrogen sulphide is then removed. For purification, the liquid MBT is brought into contact with cold carbon disulphide, with the formation of two phases, a slurry of MBT and carbon disulphide being formed. The MBT is said to have a purity of 99.5%, which merely in view of the quoted melting range of 172 to 175C (literature value for pure MBT: 180 - 182C) appears dubious. The yield was about 20% and is thus completely uneconomic.
The purity of the MBT has an effect during the conversion to the said vulcanisation accelerators.
Experiments in this regard give the following findings:
in oxidation reactions in accordance with German Patent 3,113,298 and German Patent 3,325,724 (preparation of MBTS and respectively, CBS or TBBS), MBT prepared and purified in accordance with US Patent 3,031,073 and obtained after three process cycles led to dark greasy deposits on the stirrer shaft and reactor wall. These deposits bound the catalyst and severely slowed down the reaction.
There was therefore a need for an economic process for the preparation of a highly pure MBT in high yield. The recycling of the intermediates and by-products should not have an adverse effect on the quality of the M~T such that oily deposits are formed in the oxidation reaction to give dibenzothiazolyl disulphide or sulphenamides and the reaction is substantially slowed down, which is reflected in a low space-time yield.
The object of the invention was, therefore, to provide a process in accordance with the precharacteris-ing clause which solves the problems mentioned.
The process according to the invention is charac-terised in that the reaction is carried out with a residence time in the reactor of at least 1 hour and at temperatures of 220 - 280C and said reaction is discon-tinued before the reaction equilibrium is reached and a _4_ maximum hydrogen sulphide pressure at elevated temperature is maintained on cooling by mixing the crude reaction product with carbon disulphide and the hydrogen sulphide i9 removed completely only after the crystal-lisation of the 2-mercaptobenzothiazole.
Preferably the maximum residence time tm~ as a function of the reaction temperature TR [ R] is given by the formula tm~ = 278.3 - 101 log TR hours.
From the formula a maximum residence time of 6.3 hours is calculated for a reaction temperature of 220C, a maximum residence time of 3.7 hour~ for a reaction temperature of 250C and a maximum residence time of 1.3 hours for a reaction temperature of 280C.
Residence time is understood to be the time for which the reaction mixture is kept at the reaction temperature. The reaction is discontinued before the reaction equilibrium is reached and accordingly when conversion is incomplete and is preferably discontinued very rapidly by mixing the reaction mixture with carbon disulphide, the hydrogen sulphide present in the reaction mixture not yet being removed. The reaction i~ at equi-librium when the concentration of MBT remains constant.
The maintenance of a maximum hydrogen sulphide pressure up to the time of crystallisation and the residence time limited as a function of the reaction temperature lead to a mixture of intermediates and by-product~ which, on recycling, without adjustment of the composition of the feed mixture, after a certain number of return cycles remains constant in respect of the products and their proportions. The maximum residence time must in no case be exceeded because otherwise the composition of the intermediates and by-products changes in such a way that they can no longer be converted to MBT, as a result of wh:ich the recycling into the process is impaired.
Preferably, the~ crude molten MBT is mixed with carbon disulphide in an amount such that the mixture i5 homogeneous.
h ~3.~
As a result of the combination of the process features according to the invention, yields of about 98~
with a purity of about 98% are achieved. This is the case although according to the law of mass action the amount of hydrogen sulphide remaining in the reaction mixture would have to suppress the formation of MBT.
Preferred embodLmen s of the individual features have already been indicated in the sub-claims.
Preferably, aniline, carbon disulphide and sulphur in a molar ratio of 0.8 - 1.1 : 1 - 2 : 0.8 - 1.2 are added to the recycled interm diates and bi-products and this reaction mixture is allowed to react under autogenous pressure. Optimum yields coupled with very high pusity are obtained if aniline, carbon disulphide and sulphur in a molar ratio of 0.9 - 1.1 : 1.2 - 1.7 :
0.9 - 1.1 are added to the recycled intermediates and by-products and this reaction mixture is allowed to react under autogenous pressure. These optimum results are obtained in particular if the reaction mixture is reacted at 245 - 255C and with a residence tLme of 1.5 - 2.5 hours under autogenous pressure.
When mixing the reaction mixture with CS2 after termination of the reaction, the temperature and the concentration of CS2 are to be 50 chosen that a visually clear solution with as high as possi~le a concentration of MBT is formed. In general, there are 0.7 - 10 parts by weight of CS2, preferably 0.9 to 3, per 1 part by weight of reaction mixture. For example, after the reaction has been discontinued the temperature of the reaction mixture is 180 - 200C and that of the CS2 i3 at most 100 - 140C.
The resulting temperature of the solution should preferably be above 100C in order to ensure a high MBT
concentration. The wash filtrate from the MBT purifica-tion step, which substantially consi~ts of CS2 and has a temperature of/ for example, 20 - 50~C and in general of about 35C, can also be used without further purification for preparation of the solution.
It is possible either to add the reaction mixture in a second pressure vessel to the CS2 or to add the CSz f~ t~
to the reaction mixture. The e~bodiment of the process according to the invention in which the crude reaction mixture is transferred immediately after the end of the residence time into a pressure ve~sel into which CS2 has been initlally introduced is preferred. This procedure enables the intended residence time to be maintained very accurately because as a result of the rapid cooling of the reaction mixture, the reaction is terminated immediately. Preferably, the CS2 initially introduced has a temperature of below 100C, preferably between 30 and 100C.
Even after mixing with the carbon disulphide, the crude MBT remains under the autogenous pressure of the hydrogen sulphide evolved during the reaction for forma-tion of MBT.
The homogeneous mixture is finally cooled to a temperature of between 20 and 60C, preferably within a period of between 1.5 and 4.0 hour~, the pure MBT being obtained as fine-grained crystals and the unconverted starting compounds and the by-products, and also small amounts of MBT, remaining in the mother liquor. ~2S is removed completely by letting down the pressure only after the mixture ha3 been cooled to a temperature below 80C.
Preferably, the pressure essentially generated by hydrogen sulphide is adjuste~ by letting down such that it is still at least 1.5 MPa (15 bar) after cooling to 150C and still at least 0.6 MPa (6 bar) after cooling to 100C and at temperatures below 80C approximately corresponds to the vapour pressure of the carbon disulphide.
After cooling of the ~olution, the precipitated MBT is filtered off or centrifuged off from the mother liquor, washed with approximately 1 to 3 times the amount of carbon disulphide and dried under a nitrogen atmos-phere or optionally under vacuum in a dryer at 50 -130C.
The mother liquor which is obtained after the filtration and iB in the form of a solution of s ~
unconverted aniline and sulphur, and also the by-products formed, but also small amounts of MBT, in carbon disul-phide is recycled into the process for the preparation of MBT. This way make it necessary, depending on the amount S of carbon disulphide employed for the purification, to concentrate the mother liquor. Carbon disulphide is distilled off until the amount of carbon disulphide required for the next batch remains. This carbon disul-phide and the unconverted starting materials and bi-products are then recycled into the reactor, to which,finally, fresh aniline and fresh sulphur are also fed, specifically in amounts ~uch that, without taking into account the amounts of sulphur and aniline still pre~ent in the mother liquor, the proportions of the three reactants are restored to those necessary for the MBT
synthesi~. The CS2 recovered can be re-used to prepare the solution or for washing.
It has now been found that the procedure accord-ing to the invention leads to an acceleration of the ~0 reaction to form MBT (see exa~ple 2). An autocatalytic effect can thus be assumed, because the by-products obtained according to the invention apparently accelerate the present reaction for the formation of MBT. The rea~on for this is that not only the presence of hydrogen sulphide but also the shortened reaction time lead to the con~tituents of the by-product~ of the reaction mixture being of a different composition than in the case of the prior art. This also has the advantage that the mother liquor is not loaded with impurities from ~econdary reactions or decomposition reactions and a large number of mother liquor return cycles can be carried out. The number of cycles iB virtually unlimited if a small portion of the mother liquor is removed from the circula-tion with each cycle. The preparation of MBT in a total yield of about 98~ i3 achieved according to the inven-tion.
The product purified according to the invention is obtained in the form of fine-grained material which does not dust and is free-flowing, that is to say very ~ ~ r ~J ~
easy to handle.
The present invention is illustrated in more detail by the following examples:
Example 1 A 1.3 litre pressure autoclave with a paddle stirrer was charged, in each case, with the following batch (see table):
153 g of aniline 52.6 g of sulphur, sublLmed 187.4 g of carbon disulphide (technical grade) mother liquor from the preceding experiment containing x g of solid residue The reactor was closed and heated to 250C. The residence time was 2 hours, measured from the tLme when the target temperature was reached.
After termination of the reaction, the mixture was cooled to 180C and 600 g of carbon disulphide were pumped into the reactor in the course of 20 minutes. When the addition of CS2 was complete, the reactor was cooled to 28C in the course of 2.5 hours. Only then was the pressure let down and H2S removed. The reactor was emptied and the suspension separated on a laboratory filter (vacuum filtration). The filter cake was finally rinsed wi$h about 700 g of carbon disulphide and then dried in vacuo at 50C.
The filtrate was concentrated in a rotary evapor-ator at 50C. Both the concentrated mother liquor and the carbon disulphide recovered were re-used for the next batch. The amounts of aniline and sulphur converted to MBT are replaced.
_ 9 _ S
Table 1 Cycle Recycled Yield Purity Melting Space-by-products MBT HPLC Titr point time yield _ _ (g) (g) ~ by % by (C) kg/m3h weight weight l - 159 99.7 99.4 182.7 217 2 96.4 241.7 99.2 99.2 182.8 33~
3 125.9 281.9 98.0 98.9 182.4 383 4 131.2 264.0 97.7 99.0 182.3 360 145.5 264.3 ~6.9 99.1 182.0 361 9 188.3 271.8 97.4 ~.3 181.5 371 13 241.1 2~0.5 97.0 98.9 181.1 382 243.0 270.9 97.3 98.4 181.6 359 18 239.5 265.0 97.4 98.3 180.9 362 .
The colour of the coarse crystalline MBT ranges from a very pale yellow to a pale beige.
Example 2 0.2 mol of aniline, 0.2 mol of sulphur and 0.3 mol of carbon disulphide were introduced into a pressure reactor having a capacity of 100 ml and ~tirred in said reactor, with the aid of a magnetic stirrer, at 250C and under the autogenous hydrogen sulphide pressure which is generated, for a specific time indicated in the table below. At the end of the residence tLme, the contents of the reactor were cooled rapidly, the hydrogen sulphide pressure was let down and the contents of the reactor were takPn up in methanol. The methanol solution was then evaporated to dryness. The MBT content of the solid was determined with the aid of HPLC and the total yield of the reaction was calculated from this.
Under otherwise identical conditions, further experiments were carried out in which, in each casP, mother liquor containing 25 g of interm2diates and ,~ ~3 .j O i ~
by-products, as obtained from the preparation of 2-mercaptobenzothiazole described in Example 1, was mixed into the reaction mixture. The MBT content of the mother liquor was taken into account when calculating the reaction yield.
Table 2 MBT yield ~%~
Reaction Residence With recycling Without recycling 10temperature tLme of mother of mother liquor (min) liquor (comparison) -250C 30 48 lg 250C ~0 77 43.5 250C 90 ~7.5 64.5 250C 120 93.2 74 250C 180 96.3 85.6 ~xample 3 204.9 g of aniline, 70.5 g of sulphur, 251.3 g of carbon disulphide and 375 g of by-products from an earlier cycle were reacted at 250C for a residence time of 2 hours in a 1 1 pressure autoclave. ~he residence tLme was taken a~
the time after the reaction temperature of 250~C wa~
reached.
The hot melt was transferred to a crystalliser of 2 l capacity, into which 760 g of carbon disulphide at a temperature of 108 C had been initially introduced. The mixing temperature was 145C, at which a measurable reaction no longer takes place. The transfer of the hot melt was effected under the full autogenous H2S pressure.
On cooling to room temperature at a rate of 0.8 Klmin, the MBT crystallised out, H2S being gradually removed. The solid MBT was filtered off, rinsed with 400 g of CS2 and dried in vacuo at 50C.
--ll--Example 4 (comparison example) The procedure of Example 3 was repeated except that after a residence time of 2 hours at 250C the pressure autoclave under the autogenous ~2S pressure of 56 bar was let down and H2S was thus removed before the transfer to the cry~talliser.
Ex~ple 5 (comparison example) The procedure of Example 3 was repeated, except that the residence time at the reaction temperature of 10 250C was 5 hours. In this case also the transfer to the crystalliser was made under the full autogenou~ C2S
pressure.
The product characteri~tic3 of the MBT obtained in Example~ 3, 4 and 5 are compared in Table 3, from 15 which it is seen that using the proces~ according to the invention, MBT i~ obtained not only in a high space-time yield but also in high purity.
Tahle 3 Example 3 Example 4 Example S
(comparison) (comparison) Weight of 361.6 g 341.1 g 348.9 g MBT
Appearance Powder, Powder, Powder, yellow brown brown Colour (Gardner I) (13% Na-MBT 12 18 16 solution) Purity, HPLC 97.4 % 94.9 % 95.9 %
by weight by weight by weight Purity, 98.8 % 97.2 % 97.8 %
titrimetric by weight by weight by weight Melting 180.6C 179.8C 179.7C
point Purity of 98.9 mol % 97.5 mol % 97.8 mol %
TLC
-
Industrially, M~T is generally produced by the Kelly process (US Patent 1,631,871), in which aniline, carbon disulphide and sulphur are reacted under elevated pressure at elevated temperatures. The resulting crude MBT must then be purified to remove unconverted starting compounds, intermediates and products from secondary reactions. The MBT purification which is customary industrially in principle consists of a reprecipitation, in which the crude MBT is dissolved in sodium hydroxide solution and the tar-like by-products are decanted off, filtered off or extracted. The aqueou~ sodium MBT solu- -tion is subjected to a further oxidative treatment, if appropriate; the MBT is then precipitated using sulphuric acid and filtered off (cf. German Patent 2,258,484).
The disadvantage~ of a purification of this ~ype are that the aqueous phase contains about 85 kg of Na2SOs per lOQ kg of MBT formed, which ha3 to be disposed of with the effluent. In addition, about 15 kg of waste products (tars~ are produced per 100 kg of MBT and the bulk of these waste products has to be disposed of as solid waste, for example by means of combustion. A
considerable proportion of the by-products also passes into the effluent, where it causes a high chemical oxygen demand. The chemical oxygen demand (COD) is determined in mg/l 0z by back-titration of dichromate. The analytical 7 ,', methods vary and must be indicated with the result.
In addition, in the case of modern catalytic oxidation processes using oxygen to form MBTS and sul-phenamides (compare German Patent 3,113,298 and, respec-tively, German Patent 3,325,724) a high purity of the MBT
is required because it is then possible to work with very low catalyst concentrations. Such a purity is not guaran-teed with the conventional production methods for MBT.
Those skilled in the art have therefore made many attempts to prepare MBT both in high purity and in high yield. Thus, US Patent 3,031,073 describes another process for the preparation of MBT, in which aniline, carbon disulphide and sulphur are heated under pressure in a cyclic procedure, the pressure is reduced, the ~BT
is removed from the crude product, the residue is mixed with the necessary amount of aniline, carbon disulphide and sulphur and this mixture is again heated to form MBT.
Any method is said to be suitable for isolation of MBT
from the crude reaction product. This patent specification pays detailed attention to a purification method using water/carbon disulphide emulsions, which incidentally also contain a surface-active substance.
However, according to Example 1 of the said US
Patent Specification 3,031,073, it is also possible to use carbon disulphide on its own as purifying agent.
After a reaction time of 5 hours at 245C, the reaction is discontinued by letting down the pressure and removing the reaction mixture from the autoclave. With this procedure the pre~sure generated by hydrogen sulphide is entirely removed by letting down to atmospheric pressure.
In order to purify the crude product, the latter is mixed with carbon disulphide in an autoclave and the mixture is heated to 140C and kept at this temperature for 30 to 45 minutes. Finally, based on the purification method, MBT
is obtained in a yield of 94% and in a purity which i8 indicated as 99.5%. When thiq procedure was repeated, a total yield of 82~ was obtained. The MBT had a purity of 98%.
DE-OS (German Published Application) 2,652,394 describes a process for the purification of crude MBT
using carbon disulphide. According to Example 1, aniline, carbon disulphide and sulphur are allowed to react for 50 minutes at 220C and the hydrogen sulphide is then removed. For purification, the liquid MBT is brought into contact with cold carbon disulphide, with the formation of two phases, a slurry of MBT and carbon disulphide being formed. The MBT is said to have a purity of 99.5%, which merely in view of the quoted melting range of 172 to 175C (literature value for pure MBT: 180 - 182C) appears dubious. The yield was about 20% and is thus completely uneconomic.
The purity of the MBT has an effect during the conversion to the said vulcanisation accelerators.
Experiments in this regard give the following findings:
in oxidation reactions in accordance with German Patent 3,113,298 and German Patent 3,325,724 (preparation of MBTS and respectively, CBS or TBBS), MBT prepared and purified in accordance with US Patent 3,031,073 and obtained after three process cycles led to dark greasy deposits on the stirrer shaft and reactor wall. These deposits bound the catalyst and severely slowed down the reaction.
There was therefore a need for an economic process for the preparation of a highly pure MBT in high yield. The recycling of the intermediates and by-products should not have an adverse effect on the quality of the M~T such that oily deposits are formed in the oxidation reaction to give dibenzothiazolyl disulphide or sulphenamides and the reaction is substantially slowed down, which is reflected in a low space-time yield.
The object of the invention was, therefore, to provide a process in accordance with the precharacteris-ing clause which solves the problems mentioned.
The process according to the invention is charac-terised in that the reaction is carried out with a residence time in the reactor of at least 1 hour and at temperatures of 220 - 280C and said reaction is discon-tinued before the reaction equilibrium is reached and a _4_ maximum hydrogen sulphide pressure at elevated temperature is maintained on cooling by mixing the crude reaction product with carbon disulphide and the hydrogen sulphide i9 removed completely only after the crystal-lisation of the 2-mercaptobenzothiazole.
Preferably the maximum residence time tm~ as a function of the reaction temperature TR [ R] is given by the formula tm~ = 278.3 - 101 log TR hours.
From the formula a maximum residence time of 6.3 hours is calculated for a reaction temperature of 220C, a maximum residence time of 3.7 hour~ for a reaction temperature of 250C and a maximum residence time of 1.3 hours for a reaction temperature of 280C.
Residence time is understood to be the time for which the reaction mixture is kept at the reaction temperature. The reaction is discontinued before the reaction equilibrium is reached and accordingly when conversion is incomplete and is preferably discontinued very rapidly by mixing the reaction mixture with carbon disulphide, the hydrogen sulphide present in the reaction mixture not yet being removed. The reaction i~ at equi-librium when the concentration of MBT remains constant.
The maintenance of a maximum hydrogen sulphide pressure up to the time of crystallisation and the residence time limited as a function of the reaction temperature lead to a mixture of intermediates and by-product~ which, on recycling, without adjustment of the composition of the feed mixture, after a certain number of return cycles remains constant in respect of the products and their proportions. The maximum residence time must in no case be exceeded because otherwise the composition of the intermediates and by-products changes in such a way that they can no longer be converted to MBT, as a result of wh:ich the recycling into the process is impaired.
Preferably, the~ crude molten MBT is mixed with carbon disulphide in an amount such that the mixture i5 homogeneous.
h ~3.~
As a result of the combination of the process features according to the invention, yields of about 98~
with a purity of about 98% are achieved. This is the case although according to the law of mass action the amount of hydrogen sulphide remaining in the reaction mixture would have to suppress the formation of MBT.
Preferred embodLmen s of the individual features have already been indicated in the sub-claims.
Preferably, aniline, carbon disulphide and sulphur in a molar ratio of 0.8 - 1.1 : 1 - 2 : 0.8 - 1.2 are added to the recycled interm diates and bi-products and this reaction mixture is allowed to react under autogenous pressure. Optimum yields coupled with very high pusity are obtained if aniline, carbon disulphide and sulphur in a molar ratio of 0.9 - 1.1 : 1.2 - 1.7 :
0.9 - 1.1 are added to the recycled intermediates and by-products and this reaction mixture is allowed to react under autogenous pressure. These optimum results are obtained in particular if the reaction mixture is reacted at 245 - 255C and with a residence tLme of 1.5 - 2.5 hours under autogenous pressure.
When mixing the reaction mixture with CS2 after termination of the reaction, the temperature and the concentration of CS2 are to be 50 chosen that a visually clear solution with as high as possi~le a concentration of MBT is formed. In general, there are 0.7 - 10 parts by weight of CS2, preferably 0.9 to 3, per 1 part by weight of reaction mixture. For example, after the reaction has been discontinued the temperature of the reaction mixture is 180 - 200C and that of the CS2 i3 at most 100 - 140C.
The resulting temperature of the solution should preferably be above 100C in order to ensure a high MBT
concentration. The wash filtrate from the MBT purifica-tion step, which substantially consi~ts of CS2 and has a temperature of/ for example, 20 - 50~C and in general of about 35C, can also be used without further purification for preparation of the solution.
It is possible either to add the reaction mixture in a second pressure vessel to the CS2 or to add the CSz f~ t~
to the reaction mixture. The e~bodiment of the process according to the invention in which the crude reaction mixture is transferred immediately after the end of the residence time into a pressure ve~sel into which CS2 has been initlally introduced is preferred. This procedure enables the intended residence time to be maintained very accurately because as a result of the rapid cooling of the reaction mixture, the reaction is terminated immediately. Preferably, the CS2 initially introduced has a temperature of below 100C, preferably between 30 and 100C.
Even after mixing with the carbon disulphide, the crude MBT remains under the autogenous pressure of the hydrogen sulphide evolved during the reaction for forma-tion of MBT.
The homogeneous mixture is finally cooled to a temperature of between 20 and 60C, preferably within a period of between 1.5 and 4.0 hour~, the pure MBT being obtained as fine-grained crystals and the unconverted starting compounds and the by-products, and also small amounts of MBT, remaining in the mother liquor. ~2S is removed completely by letting down the pressure only after the mixture ha3 been cooled to a temperature below 80C.
Preferably, the pressure essentially generated by hydrogen sulphide is adjuste~ by letting down such that it is still at least 1.5 MPa (15 bar) after cooling to 150C and still at least 0.6 MPa (6 bar) after cooling to 100C and at temperatures below 80C approximately corresponds to the vapour pressure of the carbon disulphide.
After cooling of the ~olution, the precipitated MBT is filtered off or centrifuged off from the mother liquor, washed with approximately 1 to 3 times the amount of carbon disulphide and dried under a nitrogen atmos-phere or optionally under vacuum in a dryer at 50 -130C.
The mother liquor which is obtained after the filtration and iB in the form of a solution of s ~
unconverted aniline and sulphur, and also the by-products formed, but also small amounts of MBT, in carbon disul-phide is recycled into the process for the preparation of MBT. This way make it necessary, depending on the amount S of carbon disulphide employed for the purification, to concentrate the mother liquor. Carbon disulphide is distilled off until the amount of carbon disulphide required for the next batch remains. This carbon disul-phide and the unconverted starting materials and bi-products are then recycled into the reactor, to which,finally, fresh aniline and fresh sulphur are also fed, specifically in amounts ~uch that, without taking into account the amounts of sulphur and aniline still pre~ent in the mother liquor, the proportions of the three reactants are restored to those necessary for the MBT
synthesi~. The CS2 recovered can be re-used to prepare the solution or for washing.
It has now been found that the procedure accord-ing to the invention leads to an acceleration of the ~0 reaction to form MBT (see exa~ple 2). An autocatalytic effect can thus be assumed, because the by-products obtained according to the invention apparently accelerate the present reaction for the formation of MBT. The rea~on for this is that not only the presence of hydrogen sulphide but also the shortened reaction time lead to the con~tituents of the by-product~ of the reaction mixture being of a different composition than in the case of the prior art. This also has the advantage that the mother liquor is not loaded with impurities from ~econdary reactions or decomposition reactions and a large number of mother liquor return cycles can be carried out. The number of cycles iB virtually unlimited if a small portion of the mother liquor is removed from the circula-tion with each cycle. The preparation of MBT in a total yield of about 98~ i3 achieved according to the inven-tion.
The product purified according to the invention is obtained in the form of fine-grained material which does not dust and is free-flowing, that is to say very ~ ~ r ~J ~
easy to handle.
The present invention is illustrated in more detail by the following examples:
Example 1 A 1.3 litre pressure autoclave with a paddle stirrer was charged, in each case, with the following batch (see table):
153 g of aniline 52.6 g of sulphur, sublLmed 187.4 g of carbon disulphide (technical grade) mother liquor from the preceding experiment containing x g of solid residue The reactor was closed and heated to 250C. The residence time was 2 hours, measured from the tLme when the target temperature was reached.
After termination of the reaction, the mixture was cooled to 180C and 600 g of carbon disulphide were pumped into the reactor in the course of 20 minutes. When the addition of CS2 was complete, the reactor was cooled to 28C in the course of 2.5 hours. Only then was the pressure let down and H2S removed. The reactor was emptied and the suspension separated on a laboratory filter (vacuum filtration). The filter cake was finally rinsed wi$h about 700 g of carbon disulphide and then dried in vacuo at 50C.
The filtrate was concentrated in a rotary evapor-ator at 50C. Both the concentrated mother liquor and the carbon disulphide recovered were re-used for the next batch. The amounts of aniline and sulphur converted to MBT are replaced.
_ 9 _ S
Table 1 Cycle Recycled Yield Purity Melting Space-by-products MBT HPLC Titr point time yield _ _ (g) (g) ~ by % by (C) kg/m3h weight weight l - 159 99.7 99.4 182.7 217 2 96.4 241.7 99.2 99.2 182.8 33~
3 125.9 281.9 98.0 98.9 182.4 383 4 131.2 264.0 97.7 99.0 182.3 360 145.5 264.3 ~6.9 99.1 182.0 361 9 188.3 271.8 97.4 ~.3 181.5 371 13 241.1 2~0.5 97.0 98.9 181.1 382 243.0 270.9 97.3 98.4 181.6 359 18 239.5 265.0 97.4 98.3 180.9 362 .
The colour of the coarse crystalline MBT ranges from a very pale yellow to a pale beige.
Example 2 0.2 mol of aniline, 0.2 mol of sulphur and 0.3 mol of carbon disulphide were introduced into a pressure reactor having a capacity of 100 ml and ~tirred in said reactor, with the aid of a magnetic stirrer, at 250C and under the autogenous hydrogen sulphide pressure which is generated, for a specific time indicated in the table below. At the end of the residence tLme, the contents of the reactor were cooled rapidly, the hydrogen sulphide pressure was let down and the contents of the reactor were takPn up in methanol. The methanol solution was then evaporated to dryness. The MBT content of the solid was determined with the aid of HPLC and the total yield of the reaction was calculated from this.
Under otherwise identical conditions, further experiments were carried out in which, in each casP, mother liquor containing 25 g of interm2diates and ,~ ~3 .j O i ~
by-products, as obtained from the preparation of 2-mercaptobenzothiazole described in Example 1, was mixed into the reaction mixture. The MBT content of the mother liquor was taken into account when calculating the reaction yield.
Table 2 MBT yield ~%~
Reaction Residence With recycling Without recycling 10temperature tLme of mother of mother liquor (min) liquor (comparison) -250C 30 48 lg 250C ~0 77 43.5 250C 90 ~7.5 64.5 250C 120 93.2 74 250C 180 96.3 85.6 ~xample 3 204.9 g of aniline, 70.5 g of sulphur, 251.3 g of carbon disulphide and 375 g of by-products from an earlier cycle were reacted at 250C for a residence time of 2 hours in a 1 1 pressure autoclave. ~he residence tLme was taken a~
the time after the reaction temperature of 250~C wa~
reached.
The hot melt was transferred to a crystalliser of 2 l capacity, into which 760 g of carbon disulphide at a temperature of 108 C had been initially introduced. The mixing temperature was 145C, at which a measurable reaction no longer takes place. The transfer of the hot melt was effected under the full autogenous H2S pressure.
On cooling to room temperature at a rate of 0.8 Klmin, the MBT crystallised out, H2S being gradually removed. The solid MBT was filtered off, rinsed with 400 g of CS2 and dried in vacuo at 50C.
--ll--Example 4 (comparison example) The procedure of Example 3 was repeated except that after a residence time of 2 hours at 250C the pressure autoclave under the autogenous ~2S pressure of 56 bar was let down and H2S was thus removed before the transfer to the cry~talliser.
Ex~ple 5 (comparison example) The procedure of Example 3 was repeated, except that the residence time at the reaction temperature of 10 250C was 5 hours. In this case also the transfer to the crystalliser was made under the full autogenou~ C2S
pressure.
The product characteri~tic3 of the MBT obtained in Example~ 3, 4 and 5 are compared in Table 3, from 15 which it is seen that using the proces~ according to the invention, MBT i~ obtained not only in a high space-time yield but also in high purity.
Tahle 3 Example 3 Example 4 Example S
(comparison) (comparison) Weight of 361.6 g 341.1 g 348.9 g MBT
Appearance Powder, Powder, Powder, yellow brown brown Colour (Gardner I) (13% Na-MBT 12 18 16 solution) Purity, HPLC 97.4 % 94.9 % 95.9 %
by weight by weight by weight Purity, 98.8 % 97.2 % 97.8 %
titrimetric by weight by weight by weight Melting 180.6C 179.8C 179.7C
point Purity of 98.9 mol % 97.5 mol % 97.8 mol %
TLC
-
Claims (12)
1. Process for the preparation of 2-mercaptoben-zothiazole from aniline, sulphur and carbon disulphide under pressure and the separation of the 2-mercaptoben-zothiazole from the crude reaction product by cooling and recycling the by-products into the reactor together with aniline, sulphur and carbon disulphide, characterised in that the reaction is carried out with a residence time in the reactor of at least 1 hour and at temperatures of 220 - 280°C and said reaction is discontinued before the reaction equilibrium is reached and a maximum hydrogen sulphide pressure is maintained on cooling by mixing the crude reaction product with carbon disulphide above 100°C
and the hydrogen sulphide is removed completely only after the crystallisation of the 2-mercaptobenzothiazole.
and the hydrogen sulphide is removed completely only after the crystallisation of the 2-mercaptobenzothiazole.
2. Process according to Claim 1, characterised in that the maximum residence time tmax is calculated as a function of the reaction temperature TR [°k] from the formula tmax = 278.3 - 101 ? log TR hours.
3. Process according to Claim 1 or 2, characterized in that aniline, carbon disulphide and sulphur in a molar ratio of 0.8 - 1.2 : 1 - 2 : 0.8 - 1.2 are added to the recycled intermediates and by products and this reaction mixture is allowed to react under autogenous pressure.
4. Process according to Claim 3, characterised in that aniline, carbon disulphide and sulphur in a molar ratio of 0.9 - 1.1 : 1.2 - 1.7 : 0.9 - 1.1 are added to the recycled intermediates and by-products and this reaction mixture is allowed to react under autogenous pressure.
5. Process according to one or more of Claims 1 to 4, characterised in that the reaction mixture is reacted at 245 - 255°C and with a residence time of 1.5 - 2.5 hours under autogenous pressure.
6. Process according to one of more of Claims 1 to 5, characterised in that the molten crude MBT is mixed with an amount of carbon disulphide such that the mixture is homogeneous.
7. Process according to one or more of Claims 1 to 6, characterised in that the crude molten 2-mercaptoben-zothiazole and the heated carbon disulphide are mixed in such a way that the mixture has a temperature above 100°C.
8. Process according to one or more of Claims 1 to 7, characterised in that the crude reaction mixture is mixed with carbon disulphide in a weight ratio of 0.7 to 10 : 1 and preferably of 0.9 to 3 : 1.
9. Process according to one or more of Claims 1 to 8, characterised in that the crude reaction mixture is transferred immediately after the end of the residence time into a pressure vessel into which CS2 has been initially introduced.
10. Process according to Claim 9, characterised in that the CS2 initially introduced has a temperature of below 100°C, preferably between 30 and 100°C.
11. Process according to one or more of Claims 1 to 10, characterised in that the mixture of crude 2-mercap-tobenzothiazole and carbon disulphide is allowed to cool to a temperature of 20 - 60°C and to crystallise within a period of between 1.5 and 4.0 hours.
12. Process according to one or more of Claims 1 to 11, characterised in that the pressure essentially generated by hydrogen sulphide is so adjusted by letting down that it is still at least 1.5 MPa (15 bar) after cooling to 150°C and still at least 0.6 MPa (6 bar) after cooling to 100°C and at temperatures below 80°C approx-imately corresponds to the vapour pressure of the carbon disulphide.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4028473A DE4028473A1 (en) | 1990-09-07 | 1990-09-07 | METHOD FOR PRODUCING 2-MERCAPTO-BENZOTHIAZOL |
| DEP4028473.5 | 1990-09-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2050783A1 true CA2050783A1 (en) | 1992-03-08 |
Family
ID=6413842
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002050783A Abandoned CA2050783A1 (en) | 1990-09-07 | 1991-09-06 | Process for the preparation of 2-mercaptobenzothiazole |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0475226B1 (en) |
| JP (1) | JPH0559027A (en) |
| CA (1) | CA2050783A1 (en) |
| DE (2) | DE4028473A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SK286026B6 (en) * | 2003-12-23 | 2008-01-07 | Duslo, A. S. | Method for obtaining 2-merkaptobenzthiazole |
| CN106565630B (en) * | 2015-10-09 | 2020-06-26 | 江苏圣奥化学科技有限公司 | Preparation method of 2-mercaptobenzothiazole |
Family Cites Families (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1631871A (en) * | 1923-08-07 | 1927-06-07 | Goodyear Tire & Rubber | Process of manufacturing mercapto-benzo-thiazole |
| US1604199A (en) * | 1924-04-04 | 1926-10-26 | Goodyear Tire & Rubber | Accelerator for the vulcanization of rubber and method of making the same |
| GB387738A (en) * | 1930-09-22 | 1933-02-16 | Naugatuck Chem Co | Process of manufacturing 2-mercaptoarylthiazoles |
| US2090233A (en) * | 1935-11-01 | 1937-08-17 | Wingfoot Corp | Process for manufacture of mercapto aryl thiazoles |
| US2247894A (en) * | 1939-08-08 | 1941-07-01 | Wingfoot Corp | Manufacture of mercaptothiazoles |
| US3031073A (en) * | 1959-05-01 | 1962-04-24 | Monsanto Chemicals | Manufacture of mercaptobenzothiazole |
| DE1919420A1 (en) * | 1969-04-17 | 1970-10-29 | Glanzstoff Ag | Process for the preparation of 2-mercaptobenzothiazole |
| NL7105735A (en) * | 1971-04-27 | 1972-10-31 | ||
| IT1025345B (en) * | 1973-11-16 | 1978-08-10 | Ici Ltd | PROCESS FOR MANUFACTURING MERCAPTOBEN ZOTHIAZOLE |
| US3975394A (en) * | 1974-11-14 | 1976-08-17 | American Cyanamid Company | Process for 2-mercaptobenzothiazole |
| JPS5831346B2 (en) * | 1976-01-14 | 1983-07-05 | 三新化学工業株式会社 | Rough 2-marker capt. Benzo. Thiazole purification method |
| CA1075245A (en) * | 1976-03-16 | 1980-04-08 | Chong-Kuang Shaw | Process for preparation of mercaptobenzothiazole |
| DE2816503C3 (en) * | 1978-04-15 | 1981-09-17 | Akzo Gmbh, 5600 Wuppertal | Process for the preparation of 2-mercaptobenzothiazole |
| DE2816407C3 (en) * | 1978-04-15 | 1981-10-29 | Akzo Gmbh, 5600 Wuppertal | Process for the preparation of 2-mercaptobenzothiazole |
| FR2450828A1 (en) * | 1979-03-06 | 1980-10-03 | Ugine Kuhlmann | MERCAPTOBENZOTHIAZOLE PURIFICATION PROCESS |
| FR2565977B1 (en) * | 1984-06-15 | 1986-08-29 | Atochem | MERCAPTOBENZOTHIAZOLE PURIFICATION PROCESS |
| DE3604705A1 (en) * | 1986-02-14 | 1987-08-27 | Bayer Antwerpen Nv | METHOD FOR THE TREATMENT OF 2-MERCAPTOBENZTHIAZOL CONTAINING TARS |
-
1990
- 1990-09-07 DE DE4028473A patent/DE4028473A1/en not_active Withdrawn
-
1991
- 1991-08-31 DE DE59102555T patent/DE59102555D1/en not_active Expired - Lifetime
- 1991-08-31 EP EP91114692A patent/EP0475226B1/en not_active Expired - Lifetime
- 1991-09-06 JP JP3226799A patent/JPH0559027A/en active Pending
- 1991-09-06 CA CA002050783A patent/CA2050783A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| EP0475226A2 (en) | 1992-03-18 |
| EP0475226B1 (en) | 1994-08-17 |
| JPH0559027A (en) | 1993-03-09 |
| DE4028473A1 (en) | 1992-03-12 |
| DE59102555D1 (en) | 1994-09-22 |
| EP0475226A3 (en) | 1992-04-22 |
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